Microelectromechanical systems (MEMS) technology has achieved wide popularity in recent years, as it provides a way to make very small mechanical structures and integrate these structures with electrical devices on a single substrate using conventional batch semiconductor processing techniques. One common application of MEMS is the design and manufacture of sensor devices. MEMS sensor devices are widely used in applications such as automotive, inertial guidance systems, household appliances, game devices, protection systems for a variety of devices, and many other industrial, scientific, and engineering systems. One example of a MEMS sensor is a MEMS angular rate sensor. An angular rate sensor, also referred to as a gyroscope, senses angular speed or velocity around one or more axes. MEMS gyroscopes are increasingly being adapted for use in the automotive industry to facilitate antiskid control and electronic stability control in anti-rollover systems.
Many MEMS angular rate sensors utilize vibrating structures that are suspended over a substrate. One such angular rate sensor is commonly referred to as a “tuning fork” angular rate sensor and typically has electrostatic drive and capacitive-type sensing. A tuning fork angular rate sensor can include a pair of drive masses and/or a pair of sense masses. The pair of drive masses are driven in phase opposition (i.e., anti-phase). In response to an external angular stimulus about an input axis, the pair of sense masses move in phase opposition by exploiting a Coriolis acceleration component. The movement of the sense masses has an amplitude that is proportional to the angular rotation rate of the angular rate sensor about the input axis.
Unfortunately, such angular rate sensors are susceptible to common mode excitations of both of the drive masses and/or both of the sense masses. Common mode excitation is a condition in which both of the drive masses and/or both of the sense masses move in the same direction and at the same amplitude due to an external stimulus (e.g., shock, vibration, spurious acceleration). The frequency of the in-phase motion (also referred to as common mode frequency) can be as low as or lower than the frequency of the anti-phase motion (also referred to as a differential mode frequency). Thus, common mode excitation (i.e., in-phase motion) can lead to inaccuracy of the angular rate sensor or can result in permanent failure of the angular rate sensor. Moreover, the potential for inaccuracy or failure of the angular rate sensor is exacerbated by the relatively low common mode frequency.